Variable electric resistance



P 26, 1944- L w. MILLER 2,358,991

VARIABLE ELECTRIC RES I STANCE Filed Nov. 13, 1945 Patented Sept. 26, 1944 VARIABLE ELECTRIC RESISTANCE Leslie William Miller, London, England, assignor to The Morgan Crucible Company, Limited,

London, England Application November 13, 1943, Serial No. 510,193 In Great Britain March 2, 1942 1:! Claims. (Cl. 201-55) This invention relates to an improved variable electric resistance especially suitable for volume control in radio reception but not necessarily limited to that application.

There is a demand at the present time, par-.

ticularly for use on aircraft, for a midget type control, as small and compact as possible, and capable of withstanding, without undue variation in its electrical characteristics, extreme conditions of humidity and temperature such as may be encountered in tropical climates.

The variable resistance or volume control, according to the invention, is of box-like construction comprising two parts fitting or telescoping together, one part, which may be called the body of the box, and which is mainly of metal, having a bearing for the operating spindle which carries a rotor contact, the bearing being provided by a bush firmly held in an aperture in the metal bottom of the body through which it passes and sealed in position by the bottom being moulded in a sandwich of moulded synthetic plastic material the top layer of which covers the inside of the bottom between the head of the bush and the side wall of the box body, and the other part, which may be called the lid; and which is made of synthetic plastic material, having on the inside a segmental resistance element or strip encircling an inner contact and on the outside terminal tags in connection through the lid with the ends of the resistance element or strip and with the inner contact respectively.

The invention is illustrated in the accompanying drawing, which is to enlarged scale, Figure 1 being a longitudinal section and Figure 2 an end view of a variable resistance made according to the invention. Figures 3 and 4 are face views and Figure 5 a dispersed view of the various parts of the resistance.

The variable resistance or volume control is of box-like construction comprising two parts fitting or telescoping together one part I, which may be called the body of the box, having a bearing 2 sealed in the bottom i thereof for the operating spindle 3 which carries a rotor contact 4, and the other part 5, which may be called the lid, having on the inside a segmental resistance element or strip 5, encircling an inner contact 1, and on the outside terminal tags 8, 9 and ill, in connection through the lid 5 with the ends of the resistance element or strip 6 and with the inner contact I respectively.

In order to seal the body i and lid 5 of the box-like construction, a ribbon H of thermoplastic or other suitable jointing material may be carried in a groove I2 round the top of the side wall of the lid 5 which will be melted, after assembly, to form a hermetic seal between the lid and the body. Further to secure the construction small flexible projections l3 on the top or the body I may be bent over the top of the lid portion.

The terminals 8, 9 and In on the top of the lid portion are preferably stamped out of metal and formed into bucket-like pieces ll having upstanding lflexible tags and mounted at the base in sockets IS in a boss l8 P jecting from t t p of the lid 5. These are secured by rivets I! passing through the lid and the parts to which they are respectively connected inside the lid, i. e., the terminals 9 and ID to the ends of the resistance element 6 and the terminal 8 to the inner contact I which may be a metal disc concentrically disposed Within the space encircled by the resistance strip. 'The terminals are prevented from rotating about the rivets by means of small projections [8 at the bottom of the sockets which engage in suitably disposed slots in the terminals.

The box body I and lid 5 of the control are preferably each of the form of a cylinder with an open end, the lid telescoping open-end downwards into the body open-end upwards. The lid may be a moulding of synthetic plastic insulating material and the body made mainly of metal.

The bearing 2 in the box body for the operating spindle 3 is provided by a bush with a flanged head I 9 on the bottom 1' of the body and an externally screwed part 28 projecting out through the bottom and serving to fix the control in the panel of an instrument board. The bush is firmly held in the aperture in the bottom I of the body through which it passes and is sealed in position by moulding the bottom in a sandwich of moulded synthetic plastic material 2!, the top layer of which covers the inside of the bottom between the head IQ of the bush 2 and the side wall of the box body I. Adjacent this side wall the depth ofthe layer of moulded plastic is preferably reduced to provide an annular channel 22 which will accommodate the bottom rim 23 of the boxlid. A film of jointing material may be interposed between the base of the rim 23 and the bottom of the channel 22; this serves to provide a seal additional or alternative to the seal produced by the material H hereinbefore mentioned. A recess or keyway 24 may be provided in the layer 2i to engage a corresponding inward projection 25 on the bottom rim 23 of the box lid to ensure that the lid is assembled in a predetermined angular relationship with the body. This projection,

which is preferably located in a gap between the ends of the resistance element 8, may also serve as a stop to limit the travel in both directions of the rotor head 4 carried by the operating spindle 3.

The layer or moulded material 2| on the underside of the bottom I of the box body may be confined in an annular recessed portion 28. The rotor contact is preferably a metal spring strip 21 pivoted in the rotor head so that the end of the strip on one side of the pivot-will bear on the resistance element ,6 while the end on the other side will bear on the disc contact 1 in the lid. The spring strip 21 may be in the form of an oval annulus pivoted across the minor axis at 28 in two upstanding walls 4' on the rotor head 4 and having the contacting portions at the ends of the major axis, these portions being bent up so that spring pressure will be exerted at the contacts. The rotor head 4 may carry a boss 29 within the oval annulus 21, coaxial with the operating spindle 3, to act as a stop to endwise movement of the spindle towards the box lid by abutting against the centre of the disc contact I in the lid if and when thespindle 3 is pushed inwards. The bottom of the rotor head 4 may have a short boss 30 surrounding the top of the spindle to bear normally on the top of the spindle bush 2 when the rotor contacts are bearing with the desired spring pressure on the contacts in the lid. I

In order that a standard rotor head may be employed for various spindles that may be desired to be used, the rotor head may be moulded so as to embed an insert 3| with a knurled head, this insert having a central hole in its lower end into which the reduced and splined end 32 of the spindle 3 may be forced and held by a tight frictional fit.

What I claim is:

1. A variable electric resistance of box-like constructlon comprising two parts fitting together, one part, which may be called the body of the box, and which is mainly of metal, having a bearing for the operating spindle which carries a rotor contact, the bearing being provided by a bush firmly held in an aperture in the metal bottom of the body through which it passes and sealed in position by the bottom being moulded in a sandwich of moulded synthetic plastic material the top layer of which covers the inside of the bottom between the head of the bush and the side wall of the box body, and the other part, which may be called the lid, and which is made of synthetic plastic material, having on the inside a segmental resistance element encircling an inner contact and on the outside terminal tags in connection through the lid with the ends of the resistance element or strip and with the inner contact respectively.

2. A variable electric resistance as claimed in claim 1 in which the body and lid of the box-like construction are sealed by thermoplastic material.

3. A variable electric resistance as claimed in claim 1 in which the body and lid of the box like construction are sealed by thermoplastic material carried in a groove round the top of the side wall of the lid.

4. A variable electric resistance as claimed in claim 1, in which the top of the body has flexible projections adapted to be bent over the top of the lid.

5. A variable electric resistance as claimed in claim 1, in which the terminals on the top of the lid are stamped out of metal and formed into bucket-like pieces having upstanding flexible tags and mounted at the base in socket members pro-i jecting from the top of the lid.

6. A variable electric resistance as claimed in claim 1, in which the terminals on the top of the lid are stamped out of metal and formed into bucket-like pieces having upstanding flexible tags and mounted at the base in socket members projecting fromv the top of the lid, said bucket-like pieces being secured by rivets passing through the lid and the parts to which they are respectively connected inside the lid.

7. A variable electric resistance of box-like construction comprising two parts fitting together, one part, which may be called the body of the box being mainly of metal and having a bearing sealed in the bottom thereof for the operating spindle which carries a rotor contact, said bearing being provided by a bush with a flange head on the bottom of the body and an externally screwed part projecting out through the bottom and serving to fix the variable resistance in the panel of an instrument board, the bush being firmly held in the aperture in the bottom of the body through which it passes and being sealed in position by moulding the bottom in a sandwich of moulded synthetic plastic material the top layer of which covers the inside of the bottom between the head of the bush and the side wall of the box body, and the other part, which may be called the lid being a moulding of synthetic plastic material and having on the inside a segmental resistance element encircling an inner contact and on the outside terminal tags in connection through the lid with the ends of the resistance element and with the inner contact respectively;

8. A variable resistance element as claimed in claim 7 in which the moulded plastic material on the underside of the box body is confined in an annular recessed portion.

9. A variable resistance element as claimed in claim 7 in which the depth of the layer of moulded plastic material adjacent the side wall of the box body is reduced to provide an annular channel accommodating the bottom rim of the box lid.

10. A variable resistance element as claimed in claim '7 in which the depth of the layer of moulded plastic material adjacent the side wall of the box body is reduced to provide an annular channel accommodating the bottom rim of the box lid, and in which a recess is provided in the layer of moulded plastic material to engage a corresponding inward projection on the bottom rim of the box lid to ensure that the lid is assembled in a predetermined angular relationship with the body.

11. A variable resistance element as claimed in claim 7 in which the depth of the layer of moulded plastic material adjacent the side wall of the box body is reduced to provide an annular channel accommodating the bottom rim of the box lid, and in which a recess is provided in the layer of moulded plastic material to engage a corresponding inward projection on the bottom rim of the box lid to ensure that the lid is assembled in a predetermined angular relationship with the body, said projection being located in a gap between the ends of the resistance element and serving as a stop to limit the travel in both directions of the rotor head carried by the operating spindle.

12. A variable electric resistance of box-like construction comprising two parts fitting together, one part, which may be called the body of the box, having a bearing sealed in the bottom thereof for the operating spindle which carries a rotor contact which is a metal spring strip in the form of an oval annulus pivoted across the minor axis in the rotor head so that the end of the strip onone side of the pivot will bear On the resistance element whilst the end of the other side will bear on the inner contact in the layer, and the other part of the box-like construction, which may be called the lid, having on the inside a segmental resistance element encircling an inner contact and on the outside terminal tag in connection through the lid with the ends of the resistance element and with the inner contact respectively.

13. A variable electric resistance as claimed in claim 12 'inwhich the rotor head carries a boss within the rotor contact and coaxial with the operatingspindle so as to act as a stop to endwise movement of the spindle towards the box lid by abutting against the centre of the inner contact in the lid if and when the spindle is pushed inwards.

14. A variable electric resistance as claimed in claim 12 in which the rotor head carries a boss within the rotor contact and coaxial with the operating spindle so as to act as a sto to endwise movement of the spindleitowards the box lid by abutting against the centre of the inner contact in the lid if and when the spindle is pushed inwards, the bottom of the rotor head is a short boss surrounding the top of the spindle to bear normally on the top oi the spindle bush when the rotor contacts are bearing with the desired spring pressure on the contacts in the lid.

15. A variable electric resistance of box-like construction comprising two parts fitting together, one part carrying a resistance element and terminals and the other part providing a bearing for the rotor head operating spindle, said rotor head being a moulding with an insert embedded in it and this insert having a hole in its lower end into which a reduced and splined end of the operating spindle is held by a tight frictional fit.

16. A variable electric resistance of box-like construction comprising two parts fitting together, one part carrying a resistance element and terminals and the other part providing a bearing for the rotor head operating spindle, said rotor head being a moulding with an insert with a knurled head embedded in it and this insert having a hole in its lower end into which a reduced and splined end of the operating spindle is held by a tight frictional fit.

17. A variable electric resistance oi box-like construction comprising two parts fitting together, one part, which may be called the body of the box,'-having a bearing sealed in the bottom thereof for the operating spindle which carries a rotor contact, and the other part, which may be called the lid, having on the inside a segmental resistance element encircling an inner contact and on the outside terminal tags in connection through the lid with the ends of the resistance element and with the inner contact respectively, said rotor contact being carried by a rotor head which is a moulding with an insert embedded in it and this insert having a hole in its lower end into which a reduced and splined end of the operating spindle is held by a tight frictional fit.

LESIJE WILLIAM MILLER. 

